A bandgap voltage is a voltage that is substantially independent of temperature, and devices generating such voltages are widely used in integrated circuits.
Generally, a circuit generating a bandgap voltage delivers an output voltage of about 1.25 volts, similar to the bandgap of silicon at the temperature of o kelvin, which is equal to 1.22 eV.
Generally, the voltage difference between two PN junctions (for example, diodes or diode-connected bipolar transistors), the current densities of which are different, allows a current proportional to absolute temperature, generally known to those skilled in the art as a “PTAT current” (PTAT being the acronym of “proportional to absolute temperature”), to be generated through a resistor.
Moreover, the voltage across the terminals of a diode or a diode-connected transistor, through which a current, such as a PTAT current, is flowing, is a voltage including a term that is inversely proportional to absolute temperature, and a second-order term, i.e., one that varies nonlinearly with absolute temperature. Such a voltage is nevertheless designated a “CTAT voltage” by those skilled in the art (CTAT being the acronym of “complementary to absolute temperature”).
A bandgap voltage may then be obtained from the PTAT and CTAT currents by suitably choosing the resistors through which these two currents flow, making it possible to cancel out the contribution of the temperature factor for a given temperature so as to make this so-called bandgap voltage theoretically independent of temperature about the given temperature.
However, in practice the CTAT voltage includes a non-linear component (i.e., its expression includes a term of the second order).
Thus, the bandgap voltage also includes a non-linear component. It is therefore not perfectly independent of temperature.
One way of improving the precision of the bandgap-voltage source would therefore be to decrease this non-linear component.
Ways to compensating for the non-linear component of the CTAT voltage already exist and, for example, implement the addition of components of various types and especially components having different temperature coefficients. However, it is currently difficult or expensive to procure components the temperature coefficients of which are different enough to produce these circuits.